A new study from Emory University researchers has found an association between traffic-related air pollution and Alzheimer’s disease in humans.
Using brain tissue donated by metro Atlanta residents, researchers evaluated their home addresses for air pollution generated by nearby traffic. The study, released Wednesday, does not prove air pollution causes Alzheimer’s, but found an association between exposure to air pollution caused by traffic and signs of Alzheimer’s in brain tissue.
Medical and environmental officials have long warned about the consequences of air pollution on respiratory and cardiac health.
The study contributes to already existing evidence that breathing pollution may lead to “plaques” or deposits in the brain — a hallmark of Alzheimer’s disease.
“It’s concerning because the reason most of the air pollution is high in Atlanta is due to traffic,” said Anke Huels, the study’s lead author and an assistant professor of epidemiology at Emory’s Rollins School of Public Health. “It’s also why we focused specifically on traffic-related air pollution exposure.“
The study is one of the first to look at the association between air pollution and signs of Alzheimer’s disease in human brain samples, she said. The findings are published in “Neurology,” the medical journal of the American Academy of Neurology.
Brain tissue used in the study was taken from 224 donors in the brain bank at Emory’s Goizeuta Alzheimer’s Disease Research Center who died before 2020. The patients had lived in urban or suburban areas in the 20-county metro area. Most of the patients were white, 59% were male, and the patients’ mean age of death was 76.
Most of the brains studied were from people who had already been diagnosed with Alzheimer’s or some other form of dementia before they died.
While the study population isn’t comparable with the general population, Huels said the study findings are still valuable because it shows pollution is associated with plaques in the brain.
More than 6.7 million U.S. residents have been diagnosed with Alzheimer’s disease, including at least 150,000 Georgians.
Alzheimer’s, one of the dementias, is a progressive disease that affects memory and other brain functions, according to the Alzheimer’s Association. Researchers do not know the exact cause of Alzheimer’s disease, but it likely is due to a variety of genetic and environmental factors. Air pollution has been suspected previously as a potential factor.
“In our study we used air pollution models, which can give us an estimate of the residential traffic-related air pollution concentration with a very fine resolution up to 200 to 250 meters,” Huels said. “Of course you would see the highest levels of these pollutants around major highways, so people who lived very close to major highways had the highest exposure to traffic-related pollutants.”
The study looked at “fine particulate matter” from traffic exhaust and whether there was an association between breathing polluted air and signs of Alzheimer’s in the brain. According to the Environmental Protection Agency, particulate pollution is made up of tiny particles of solids or liquids so small they can be inhaled deep into the lungs and enter the bloodstream, potentially causing health problems. They are the cause of haze in some parts of the U.S.
Huels said the findings are in line with previous studies, which have shown associations between particulate pollution and cognitive decline, memory loss or a diagnosis of Alzheimer’s disease.
Researchers also looked at patients who carried the “APOE gene” a major genetic risk factor for developing Alzheimer’s. But the strongest association between pollution and Alzheimer’s was seen in those without that risk factor. This suggests that environmental factors like air pollution could be a contributing factor to Alzheimer’s disease in patients in which the disease cannot be explained by genetics.
“We know that air pollution is bad for our health, including our brains,” according to a statement from Jill Disney, program director for the Alzheimer’s Association Georgia Chapter. “Multiple studies presented during AAIC 2021 were the first to suggest that reducing pollution is associated with lower risk of dementia and Alzheimer’s disease.”
Disney called for more research in areas of the United States with high levels of pollution that tend to be populated by low income individuals and people of color.
The Chicago-based Alzheimer’s Association last year said it invested $100 million into dementia research, the largest single-year investment since 1980 when the nonprofit was founded. In Georgia alone, $600,000 was awarded to advance research efforts in 2023.
Overall, the state of Georgia has 19 ongoing projects totaling nearly $3.5 million and includes research being conducted including looking at risk factors, care and early detection.
The Emory study was funded by an Alzheimer’s Disease Research Center pilot grant through the National Institute of Aging. Huels and other researchers had no relevant financial interest in the outcome.
What is “fine particulate matter”?
According to the Environmental Protection Agency, these are tiny particles that are so small they can be inhaled deep into the lungs and enter the bloodstream, potentially causing health problems. They are the cause of haze in some parts of the U.S.
These particles are made up of solids or liquid droplets with diameters that are generally 2.5 micrometers and smaller.
How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.
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